gf-core/transfer/examples/bool.tr

data Bool : Type where 
	True : Bool
	False : Bool;

depif : (A:Type) -> (B:Type) -> (b:Bool) -> A -> B -> if Type b then A else B
depif _ _ True x _ = x
depif _ _ False _ y = y

not : Bool -> Bool
not b = if b then False else True